The present invention relates to a single functional apparatus, such as a printer, a copier and a facsimile, and a compound image forming apparatus having the abovementioned functions, and specifically relates to a technology for stably supplying an electric power to the image forming apparatus, which consumes a large amount of electric power, corresponding to variations of loading needs (electric power consumption).
Generally speaking, as shown in FIG. 8, in a conventional image forming apparatus, an AC electric power source 1 is coupled to an electric power inlet of the image forming apparatus through an AC cord 3 so as to supply the AC electric power of 100 V into a transformer 13. The transformer 13 transforms the inputted voltage to supply the electric power to a load 8. The load 8 of the image forming apparatus includes a fixing section 8a having a heater driven by the AC electric power for conducting the heat fixing operation, a control/processing section 8b driven by a DC electric power and including a control section provided with a CPU (Central Processing Unit), a storage, etc. for controlling various kinds of sections, and other processing sections. A heater driving section 6 receives the AC electric power fed from a secondary winding of the transformer 13 so as to supply a predetermined AC electric power to the fixing section 8a to control it. An AC-to-DC converting section 7 also receives the AC electric power fed from a secondary winding of the transformer 13, and rectifies the AC electric power in a rectifying section 7a, and converts the voltage of the rectified DC electric power to a predetermined DC voltage in order to supply it into the control/processing section 8b. 
Generally speaking, the allowable value of electric power to be fed through a single AC electric power cord is set at 100V-15 A in Japan. However, the recent image forming apparatus tends to inevitably consume electric power larger than the above. Accordingly, there have been proposed various kinds of countermeasures to cope with the problem mentioned in the above, so far.
For instance, Patent documents 1 and 2 (Tokkai 2003-244359 and Tokkai 2003-295702, Japanese Non-Examined Patent Publications) set forth a method for allotting a plurality of AC electric power cords to a plurality of divided loads, respectively. According to the abovementioned method, an AC electric cord is allotted to the fixing section 8a, while another AC electric cord is allotted to the control/processing section 8b. Further, to solve the safety problem of the apparatus when the AC electric cord is coupled to the electric power source, while the other AC electric cord is not coupled to the electric power source, a relay provided for turning ON/OFF the connection between the AC electric cord and the electric power source is controlled so as to secure the safety of the apparatus.
Further, Patent Document 3 (Tokkai 2003-323085, Japanese Non-Examined Patent Publication) sets forth a method in which a plurality of AC electric power cords are provided as described in the Patent Document 1, and the load is divided into a plurality of blocks which are coupled to the plurality of AC electric power cords through the switches, so that the electric power is supplied to each of the plurality of blocks from any one of the plurality of AC electric power cords. Then, by changing over the switches corresponding to each of the operating modes, electric power consumptions of which are different from each other, such as a start-up mode and a deactivating mode of the fixing apparatus, etc., the load to be coupled to the AC electric power cord is changed over corresponding to the electric power consumption.
Further, in the technology set forth in Patent Document 4 (Tokkai 2005-121681, Japanese Non-Examined Patent Publication), as described in Patent Document 1, an individual AC electric power cord is allotted to each of a plurality of loads. Further, the image forming apparatus is provided with a defect detecting mechanism for detecting an abnormality of the electric power controlling element for controlling the electric power supply, and/or a mechanism for detecting an abnormality of the electric power controlling element of the heater of the fixing device, in order to secure the safety of the apparatus.
According to the abovementioned conventional technologies in which each of the AC electric power cords are adaptively coupled, corresponding to each of the loads equipped in the image forming apparatus serving as an electro-mechanical apparatus whose electric power consumption widely varies with its operating mode, it is impossible to conduct such the electric power adjustment, corresponding to the electric power variations, that the electric power is supplied from a first AC electric power cord instead of a second electric power cord, even if the electric power consumption of the load coupled to the second electric power cord is large, while the electric power consumption of the load coupled to the first electric power cord is small. To solve the above problem, in the technology set forth in the Patent Document 3, the electric power adjustment is conducted by changing over the relationships between the plurality of AC electric power cords and the plurality of loading blocks corresponding to each of the operating modes.
In the technology set forth in the Patent Document 3, however, only the electric power adjustment corresponding to the operating modes established in advance can be conducted as mentioned in the above. In addition, in this case, it is necessary to investigate even instantaneous electric power consumption at the start-up time of the operation, by probing the operating modes and the loading blocks in advance, and the change-over operation of the AC electric power cord conducted during the activated state of the image forming apparatus has been liable to induce various problems.